This invention relates generally to road surface removal or reclaimer-stabilizer equipment and mining equipment, and more particularly, to cutter bit holders and bit blocks used in such road milling, mining, and trenching equipment.
Cutter bits are utilized in road, off-road and mining machinery on the perimeter and across the width of a rotary drum or on the outside of a continuous chain or the like where the bits are moved through an orbit which is intercepted by the face of the material being removed or recycled. Road milling equipment removes the defective surface of a road and smooths the top of all or selected portions of the road surface. The bits include a tip and a shank. The shank is received and may axially rotate in a bit holder which is secured onto a bit block that, in turn, is mounted on the drum. Each of the bits has a hardened tip, preferably made of tungsten carbide or such other hardened material that acts to remove a portion of the surface it contacts. By using a sufficient number of these bits around the outer surface of a rotating drum, a large amount of surface may be worked. Any surface being worked generally has a hardness which can be measured or anticipated prior to the removal operation. However, such road surfaces, or surfaces being removed have hardened irregularities running therethrough. The toughness or hardness of the irregularities may result in the breakage of the bits and holders as they are being run over such irregularities.
Additionally, as bits and bit holders wear during the removal process, that wear may be uneven. It would be desirable to be able to selectably change the radial orientation of the bit holder in the bit block. U.S. Pat. No. 5,106,166 discloses a bit retaining sleeve (bit holder) having four flats positioned at 90 degree orientations therearound which fit onto a flat fixation surface on the bit holder to allow the worn bit holder to be positioned in one of four radial orientations in the bit block. A need has developed for an improved means for positioning and mounting a bit holder in a bit block that provides for changing the radial orientation of the bit holder in the bit block as the holder becomes worn.
Further, a need has developed for providing ease of removability of bits in their bit holders, especially when the bit becomes worn and need to be replaced. U.S. Pat. No. 5,374,111 discloses an undercut flange at the bottom of a base of a bit that allows a pry bar to be wedged between that flange and the top of the bit block (no bit holder in this patent) to help remove a bit from a bit block. It would be desirable to provide a more efficient means for allowing the removal of a bit from a bit holder or a bit block.
Additionally, tightening a small fastener on the bottom of a bit holder to hold it in the bit block concentrates friction forces on a small area of the nut top face and the bottom of the bit block. It would be desirable to spread those friction forces over a larger area.
It is, therefore, an object of the present invention, generally stated, to provide an improved means for quickly removing a bit from its bit holder, or a bit block if a bit holder is not utilized.
Another object of the present invention is the provision of an improved means for changing the radial orientation of the mounting of a bit holder on a bit block.
Another object of the invention is the provision of an improved means for providing for breakage of inexpensive replaceable parts when road resurfacing equipment and mining equipment bits encounter very hard irregularities in the surface being milled or mined.
The invention is directed to a bit assembly for use in road milling and mining equipment. The bit assembly includes a bit having a hardened distal end connected to a shank portion and means including a shank receiving bore for mounting the bit on that equipment. The invention resides in an improvement comprising a reduced cross section means on one of the bit and the means for mounting the bit on the equipment. This reduced cross section means provides a predetermined area of failure for when the bit contacts a hard discontinuity in material it encounters.
The invention is further directed to a bit holder for retaining a bit therein as a part of a bit assembly. The bit holder comprises a generally frustoconical bit mounting portion including a top surface, a mediate portion tapering outwardly from the top surface and a radial flange defining the bottom thereof. The shank portion extends axially from the radial flange and terminates in a fastening portion adjacent a distal end of the shank. An axial bore is in communication with and extends inwardly from the top surface and is adapted for mounting a bit therein. The invention resides in indent means extending radially inwardly from an outer surface of the mediate portion and in communication with the top surface. The indent means provides access to an underside of any bit mounted on the bit holder and resting on the top surface thereof to aid in any removal of a bit from the bit holder and provides for axially turning the bit holder with respect to the bit block.